Engineering opposite electronic polarization of singlet and triplet states increases the yield of high-energy photoproducts
Engineering opposite electronic polarization of singlet and triplet states increases the yield of high-energy photoproducts
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对单线态和三线态的相反电子极化进行工程设计可提高高能光产物的产量
DOI：
10.1073/pnas.1901752116
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Therien, Michael J.
中科院分区：
文献类型：
--
作者：
Polizzi, Nicholas F.;Jiang, Ting;Beratan, David N.;Therien, Michael J.
有效的光合能量转换需要定量、光驱动的高能、电荷分离态的形成。然而，高位激发态的能量很少被提取，部分原因是激发态流形中拥挤的态密度导致快速失活。传统的光系统设计通过将激发的供体电子密度向受体极化（“单向”ET）来促进电子转移（ET），这是一种正向设计的形式。奇怪的是，明确避免不需要的副反应的消极设计策略尚未得到充分探索。我们在这里报告，分子发色团的电子极化可以用作光驱动反应中的正和负设计元素。有趣的是，对极化激发态的谨慎设计可以引导“U 型转弯” ET（供体的激发电子密度最初被推离受体），从而超越传统的单向 ET 方案。我们通过连接的供体-受体（DA）组装直接比较单向和 U 形 ET 策略，其中选择性光学激发产生朝向或远离受体偏振的供体激发态。 DA 的超快光谱指出了实现具有相反电子极化的供体单线态和三线态激发态以关闭系间窜越的重要性。这些结果表明，相反极化的电子激发态可用于通过将这些激发态远离光合作用死胡同的状态来引导光激发态产生有用的高能产物。
Efficient photosynthetic energy conversion requires quantitative, light-driven formation of high-energy, charge-separated states. However, energies of high-lying excited states are rarely extracted, in part because the congested density of states in the excited-state manifold leads to rapid deactivation. Conventional photosystem designs promote electron transfer (ET) by polarizing excited donor electron density toward the acceptor (“one-way” ET), a form of positive design. Curiously, negative design strategies that explicitly avoid unwanted side reactions have been underexplored. We report here that electronic polarization of a molecular chromophore can be used as both a positive and negative design element in a light-driven reaction. Intriguingly, prudent engineering of polarized excited states can steer a “U-turn” ET—where the excited electron density of the donor is initially pushed away from the acceptor—to outcompete a conventional one-way ET scheme. We directly compare one-way vs. U-turn ET strategies via a linked donor–acceptor (DA) assembly in which selective optical excitation produces donor excited states polarized either toward or away from the acceptor. Ultrafast spectroscopy of DA pinpoints the importance of realizing donor singlet and triplet excited states that have opposite electronic polarizations to shut down intersystem crossing. These results demonstrate that oppositely polarized electronically excited states can be employed to steer photoexcited states toward useful, high-energy products by routing these excited states away from states that are photosynthetic dead ends.
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通讯作者：
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